1. Field of the Invention
The present invention relates to an organic light-emitting diode.
2. Description of Related Art
Organic light-emitting diodes (OLEDs) are self-emitting devices that have advantages such as a wide viewing angle, good contrast, quick response times, high brightness, and good driving voltage characteristics. OLEDs can provide multicolored images.
In general, an OLED has a structure including a substrate, and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode are sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic layers formed of organic compounds.
An operating principle of an OLED is as follows: when a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from the excited state to the ground state, light is emitted.
According to conventional OLED manufacturing processes, a patterning process needs to be performed on each of a plurality of pixel units, thus requiring a patterning process to be performed by at least three deposition or transferring processes. In addition, micro-patterns need to be formed in each pixel unit, and thus misalignment of the micro-patterns may occur. Furthermore, since holes move faster than electrons in each pixel unit, a process of forming a hole blocking layer on an emission layer to prevent the movement of holes may be further performed. To address these problems, a structure in which a blue emission layer is formed as a common layer in an upper portion or lower portion of the emission layer has been introduced.
FIG. 1 is a schematic cross-sectional view of a conventional organic light-emitting diode (OLED) 100. A first organic emission layer 131 emits red visible rays, a second organic emission layer 132 emits green visible rays, and a third organic emission layer 133 emits blue visible rays.
The third organic emission layer 133 is stacked on a hole transport layer (HTL) 122 over a first sub-pixel SP1, a second sub-pixel SP2, and a third sub-pixel SP3. The first organic emission layer 131 is formed on the third organic emission layer 133 in the first sub-pixel SP1, and the second organic emission layer 132 is formed on the third organic emission layer 133 in the second sub-pixel SP2.
Alternatively, the third organic emission layer 133 is stacked as a common layer on the HTL 122 over the first sub-pixel SP1, the second sub-pixel SP2, and the third sub-pixel SP3. A second optical thickness auxiliary layer (not shown) is formed on the third organic emission layer 133 over the first sub-pixel SP1 and the second sub-pixel SP2. A first optical thickness auxiliary layer (not shown) is formed on the second optical thickness auxiliary layer in the first sub-pixel SP1. The second organic emission layer 132 is formed in the second sub-pixel SP2, and the first organic emission layer 131 is formed on the first optical thickness auxiliary layer (not shown) in the first sub-pixel SP1. When an OLED having such a structure (in which the blue emission layer is disposed as a common layer in a lower portion of the emission layer) is manufactured, the number of patterning processes decreases due to the formation of the blue emission layer as a common layer. However, the characteristics of the OLED, in particular, the green diode are degraded, and thus, the lifetime of the green diode is shortened.